1. Field of the Invention
This invention relates to an improved process for the purification of dialkyl phosphorodithioic acid esters, and more specifically relates to the purification of a reaction mixture resulting from the reaction of an 0,0-dialkyl phosphorodithioic acid and an organic chloride.
2. Related Information
U.S. Pat. No. 2,725,828 to Diveley et al. discloses that certain esters of dithiophosphoric acid have excellent insecticidal properties and can be prepaed by the substitution reaction of an 0,0-dialkyl dithiophosphoric acid with a dichlorodioxane. This patent further discloses that the resulting product was purified by washing sequentially with water, dilute sodium hydroxide and then with water.
An article entitled "Two Organophosphorus Derivatives of p-Dioxane with Insecticidal and Acaricidal Activity" by W. R. Diveley, A. H. Haubein, A. D. Lohr and P. B. Moseley, J. Am. Chem. Soc. 81, pp. 139-144 (1959) discloses the preparation of 2,3-para-dioxanedithiol S,S-bis(0,0-diethyl phosphorodithioate)(dioxathion) from 2,3-dichloro-paradioxane and the appropriate 0,0-dialkyl hydrogen phosphorodithioates in the presence of molecular equivalents of certain bases or catalytic quantities of certain catalysts, or from para-dioxene and bis-(dialkoxyphosphinothioyl) disulfide in the presence of catalytic quantities of iodine. In one of these processes, the resulting salt was removed by filtration and the filtrate washed with 5% sodium hydroxide twice with 15% brine. ln another of these processes the reaction mixture was worked up by washing with 1% hydrochloric acid in 15% brine, and then neutralized with 10% sodium hydroxide using phenolphthalein indicator.
U.S. Pat. No. 2,815,850 (Speck, Dec. 3, 1957) discloses the use of a metal chloride from the group consisting of zinc chloride, ferrous chloride and stannous chloride to catalyze the reaction between 0,0-dialkyl dithiophosphoric acids and chloro-organic compounds wherein a chlorine is replaced by an ortho,ortho-dialkyl dithiophosphoric acid radical. The reaction products were purified by sequentially washing the reaction mixture with water, sufficient aqueous sodium hydroxide to neutralize the acids present, and finally with fresh water.
U.S. Pat. No. 4,283,885 (Minn, Aug. 11, 1981) discloses a process for improving the yield of dialkyl dithiophosphoric acid esters produced by the Lewis acid catalyzed reaction of an 0,0-dialkyl dithiophosphoric acid and an organic chloride. More specifically, the method discloses the improvement wherein the reaction is carried out in the presence of an anhydride of a fatty acid containing 2-5 carbon atoms. It was noted that the purity of the ester end-product could be improved by conducting the reaction in the presence of specified amounts of certain carboxylic acid anhydrides. The reaction mixture was washed with an acidic brine solution and then with dilute caustic to further purify the reaction mixture.
U.S. Pat. No. 4,283,338 (Minn, Aug. 11, 1981) discloses a method for improving the yield of dialkyl dithiophosphoric acid esters produced by the Lewis acid catalyzed reaction of an 0,0-dialkyl dithiophosphoric acid and an organic chloride. More specifically, the process discloses the improvement wherein the reaction is conducted under sufficient pressure to maintain the liberated hydrogen chloride in the reaction system during the course of the reaction. The reaction mixture was purified by washing with brine and then dilute alkali.
U.S. Pat. No. 4,282,153 (Minn, Aug. 4, 1981) discloses a method for improving the yield of insecticidal compositions produced by reacting an 0,0-dialkyl dithiophosphoric acid with a chloro-para-dioxane in the presence of a Lewis acid catalyst and a stoichiometric excess of the acid reactant. More specifically, the process discloses the improvement wherein certain bicyclo-heptenes are added to the system resulting from the reaction and reacted with the excess of 0,0-dialkyl dithiophosphoric acid present in the system. In this process the final reaction mixture was also washed with an acidic salt solution of hydrochloric acid and sodium chloride and then with aqueous sodium hydroxide for further purification.